Hand-held radio equipment is often used in public safety and during an emergency it is often desirable to connect the hand-held radio to a telephone network. In recent times, telephone networks are implementing a new communication technique commonly referred to as Voice over IP, where voice communication is communicated using an Internet Protocol (IP) network. The Voice over IP community has adopted Session Initiation Protocol (SIP) as a protocol of choice for signaling. SIP is a signaling protocol used for establishing sessions in an IP network and is an RFC standard (RFC 3261) understood by those skilled in the art. Using SIP, telephony becomes another web application and integrates with other Internet services.
In public safety applications, it is often desirable to interface hand-held radio equipment to a telephony network through a so called Radio-to-SIP adapter. Such hand-held radio equipment which typically operate in half-duplex lacks a means of being controlled by the calls through the SIP network without requiring operator intervention of some type.
It is desirable to provide a technique where radio calls from the network using SIP can control the activation of the radio transceiver switching the transceiver from receive to transmit and back to receive again when the party on the telephony network wishes to speak.